contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/MongoScanBatchCreator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.drill.exec.store.mongo;

import java.util.LinkedList;
import java.util.List;

import org.apache.drill.common.exceptions.ExecutionSetupException;
import org.apache.drill.common.expression.SchemaPath;
import org.apache.drill.exec.ops.ExecutorFragmentContext;
import org.apache.drill.exec.physical.base.GroupScan;
import org.apache.drill.exec.physical.impl.BatchCreator;
import org.apache.drill.exec.physical.impl.ScanBatch;
import org.apache.drill.exec.record.RecordBatch;
import org.apache.drill.exec.store.RecordReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Preconditions;

public class MongoScanBatchCreator implements BatchCreator<MongoSubScan> {
  static final Logger logger = LoggerFactory
      .getLogger(MongoScanBatchCreator.class);

  @Override
  public ScanBatch getBatch(ExecutorFragmentContext context, MongoSubScan subScan,
      List<RecordBatch> children) throws ExecutionSetupException {
    Preconditions.checkArgument(children.isEmpty());
    List<RecordReader> readers = new LinkedList<>();
    for (BaseMongoSubScanSpec scanSpec : subScan.getChunkScanSpecList()) {
      try {
        List<SchemaPath> columns = subScan.getColumns();
        if (columns == null) {
          columns = GroupScan.ALL_COLUMNS;
        }
        readers.add(new MongoRecordReader(scanSpec, columns, context, subScan.getMongoStoragePlugin()));
      } catch (Exception e) {
        logger.error("MongoRecordReader creation failed for subScan: {}.", subScan);
        logger.error(e.getMessage(), e);
        throw new ExecutionSetupException(e);
      }
    }
    logger.info("Number of record readers initialized : {}", readers.size());
    return new ScanBatch(subScan, context, readers);
  }

}